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Title: Direct Evidence of a Light-Dependent Sink of Superoxide within Chromophoric Dissolved Organic Matter
Superoxide (O2• –) is produced photochemically in natural waters by chromophoric dissolved organic matter (CDOM) via the reaction of molecular oxygen with photoproduced one-electron reductants (OERs) within CDOM. In the absence of other sinks (metals or organic radicals), O2• – is believed to undergo primarily dismutation to produce hydrogen peroxide (H2O2). However, past studies have implicated the presence of an additional light-dependent sink of O2• – that does not lead to H2O2 production. Here, we provide direct evidence of this sink through O2• – injection experiments. During irradiations, spikes of O2• – are consumed to a greater extent (∼85–30% loss) and are lost much faster (up to ∼0.09 s–1) than spikes introduced post-irradiation (∼50–0% loss and ∼0.03 s–1 rate constant). The magnitude of the loss during irradiation and the rate constant are wavelength-dependent. Analysis of the H2O2 concentration post-spike indicates that this light-dependent sink does not produce H2O2 at low spike concentrations. This work further demonstrates that simply assuming that the O2• – production is twice the H2O2 production is not accurate, as previously believed.  more » « less
Award ID(s):
1924763
PAR ID:
10538916
Author(s) / Creator(s):
; ;
Publisher / Repository:
American Chemical Society
Date Published:
Journal Name:
Environmental Science & Technology
Volume:
57
Issue:
49
ISSN:
0013-936X
Page Range / eLocation ID:
20627 to 20635
Subject(s) / Keyword(s):
Photodegradation Irradiation Superoxide Decay Pathways Decay Modeling
Format(s):
Medium: X
Sponsoring Org:
National Science Foundation
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